CVE-2025-54143 Overview
CVE-2025-54143 is a critical sandbox bypass vulnerability in Mozilla Firefox for iOS that allows sandboxed iframes on webpages to potentially download files to the device, bypassing the expected sandbox restrictions declared on the parent page. This Protection Mechanism Failure (CWE-693) enables attackers to circumvent browser security controls designed to isolate untrusted content.
Critical Impact
Attackers can leverage malicious webpages with sandboxed iframes to initiate unauthorized file downloads to iOS devices, bypassing browser sandbox restrictions and potentially delivering malware or unwanted content without user awareness.
Affected Products
- Mozilla Firefox for iOS versions prior to 141
- Firefox mobile browser installations on iPhone/iPad devices
- iOS devices running vulnerable Firefox versions
Discovery Timeline
- August 19, 2025 - CVE-2025-54143 published to NVD
- August 21, 2025 - Last updated in NVD database
Technical Details for CVE-2025-54143
Vulnerability Analysis
This vulnerability represents a Protection Mechanism Failure where the browser's iframe sandboxing implementation fails to properly enforce download restrictions. When a webpage embeds content within a sandboxed iframe using the HTML5 sandbox attribute, the iframe should be restricted from performing certain actions, including initiating downloads. However, Firefox for iOS does not properly enforce these restrictions, allowing content within sandboxed iframes to bypass the declared security constraints and trigger file downloads to the device.
The vulnerability is particularly concerning because sandboxed iframes are commonly used by web developers as a security boundary to isolate third-party content, advertisements, or untrusted user-generated content. The expectation is that this content cannot perform potentially harmful actions like downloading files.
Root Cause
The root cause of CVE-2025-54143 lies in improper enforcement of the HTML5 sandbox attribute restrictions within the Firefox for iOS download handling code path. When the browser processes download requests originating from iframe contexts, it fails to properly verify whether the initiating frame has the necessary permissions (specifically, the allow-downloads sandbox flag) before proceeding with the download operation.
This represents a gap between the security policy declared by the parent page and the actual enforcement within the browser's download subsystem. The iOS-specific implementation of Firefox appears to have a code path that does not properly check sandbox flags before allowing download operations to proceed.
Attack Vector
An attacker can exploit this vulnerability through the following attack scenario:
- The attacker hosts a malicious webpage or injects malicious content into a website
- The malicious page embeds an iframe with restrictive sandbox attributes (not including allow-downloads)
- Content within the sandboxed iframe initiates a download operation
- Due to the vulnerability, Firefox for iOS processes the download despite sandbox restrictions
- Malicious files are downloaded to the victim's device without proper authorization
This attack requires no privileges and can be executed remotely over the network. The victim needs only to visit a malicious webpage with Firefox for iOS. Once the page loads, the download can be triggered automatically without additional user interaction, making this a particularly dangerous vulnerability for drive-by download attacks targeting mobile users.
Detection Methods for CVE-2025-54143
Indicators of Compromise
- Unexpected file downloads appearing on iOS devices after browsing sessions
- Downloaded files from domains or sources that should have been sandboxed
- Unusual download activity in Firefox for iOS browsing history
- Presence of suspicious files in the iOS Files app or Downloads folder
Detection Strategies
- Monitor for unexpected download operations from Firefox for iOS on managed devices
- Implement web filtering to block known malicious domains that may exploit this vulnerability
- Review MDM logs for unusual file download patterns on iOS devices with Firefox installed
- Deploy network traffic analysis to identify suspicious download behaviors originating from sandboxed content
Monitoring Recommendations
- Enable enhanced logging for web browser activity on enterprise-managed iOS devices
- Configure alerts for file downloads from untrusted or unknown sources
- Monitor for security advisories from Mozilla regarding exploitation of this vulnerability
- Track Firefox for iOS version deployment across your device fleet to ensure compliance
How to Mitigate CVE-2025-54143
Immediate Actions Required
- Update Firefox for iOS to version 141 or later immediately
- Consider temporarily restricting Firefox for iOS usage on sensitive enterprise devices until patching is complete
- Implement web filtering to block access to known malicious sites
- Review recent download activity on devices that may have been exposed
Patch Information
Mozilla has addressed this vulnerability in Firefox for iOS version 141. Organizations and users should update to this version or later to remediate the vulnerability. The security advisory MFSA-2025-60 provides official details from Mozilla regarding this fix.
Additional technical details can be found in Mozilla Bugzilla Report #1912671.
Workarounds
- Use alternative browsers on iOS until Firefox can be updated to version 141
- Avoid browsing untrusted websites with vulnerable Firefox for iOS versions
- Enable iOS Screen Time or MDM restrictions to limit browser access on sensitive devices
- Implement network-level protections to block potentially malicious downloads
# Verify Firefox for iOS version via MDM
# Ensure all devices report Firefox version >= 141
# Example: Check managed app versions in your MDM console
# Update deployment policies to require Firefox for iOS 141+
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
